In multicast/broadcast applications, data are transmitted from a server or base station (BS) to multiple receivers over wired and/or wireless networks. Herein, a “/” is used to indicate alternative names for the same or similar components. A multicast system as used herein is a system in which a server transmits the same data to multiple receivers simultaneously, where the receivers form a subset of all the receivers up to and including all of the receivers. A broadcast system is a system in which a server transmits the same data to all of the receivers simultaneously. That is, a multicast system by definition can include a broadcast system.
Resource allocation for unicast in OFDMA systems has been widely studied. Compared with unicast, resource allocation for multicast in OFDMA systems has not drawn much attention. However, multimedia applications are bandwidth demanding and unicast does not scale well. As a result, multicast is going to play an important role in such applications. In prior art resource allocation schemes for multicast systems, the multicast rate has been defined as the total throughput of the system. In prior art solutions, though multiple users can receive data from one sub-channel, there is no concept of multicast group among which users can receive the same data from a multicast application, this resulted in high rates to some users and corresponding low rates to other users. Furthermore, supplying different rates to different users leads to a fairness issue among users. Although, the prior art captured fairness to some extent, instantaneous fairness is not guaranteed for each channel realization. As a result, prior art schemes resulted in low common data rate and lack of fairness among users.
In the present invention it is assumed in a wireless multicast application, the multicast data needs to be received reliably by all users who join the multicast group. The multicast rate is the minimum data rate that can be received by all the users. Thus, a goal of the resource allocation scheme of the present invention is to maximize the multicast rate in a wireless OFDMA communication system.
The method of the present invention takes a two-step approach to solve the resource allocate problem. In the first step, sub-channel allocation is found using a low complexity suboptimal method assuming equal power is allocated to all sub-channels. In the second step, power allocation, which can also be interpreted as bit loading, is found using another low complexity suboptimal algorithm.